The emergence of a former Guantánamo Bay detainee as the deputy leader of Al Qaeda’s Yemeni branch has underscored the potential complications in carrying out the executive order President Obama signed Thursday that the detention center be shut down within a year.

The militant, Said Ali al-Shihri, is suspected of involvement in a deadly bombing of the United States Embassy in Yemen’s capital, Sana, in September. He was released to Saudi Arabia in 2007 and passed through a Saudi rehabilitation program for former jihadists before resurfacing with Al Qaeda in Yemen.

His status was announced in an Internet statement by the militant group and was confirmed by an American counterterrorism official.

“They’re one and the same guy,” said the official, who insisted on anonymity because he was discussing an intelligence analysis. “He returned to Saudi Arabia in 2007, but his movements to Yemen remain unclear.”

The development came as Republican legislators criticized the plan to close the Guantánamo Bay, Cuba, detention camp in the absence of any measures for dealing with current detainees. But it also helps explain why the new administration wants to move cautiously, taking time to work out a plan to cope with the complications.

Almost half the camp’s remaining detainees are Yemenis, and efforts to repatriate them depend in part on the creation of a Yemeni rehabilitation program — partly financed by the United States — similar to the Saudi one. Saudi Arabia has claimed that no graduate of its program has returned to terrorism.

“The lesson here is, whoever receives former Guantánamo detainees needs to keep a close eye on them,” the American official said.